Recently, consideration for the environmental protection such as reduction of carbon dioxide emission has been socially requested. Specifically, a demand for fuel efficiency in automobiles has been increased. For such a circumstance, as a material for tires for automobiles, particularly a material for a tire tread contacting the ground, development of a material exhibiting low rolling resistance has been demanded. On the other hand, from the viewpoint of safety, development of a material exhibiting excellent wet skid resistance, and practically sufficient abrasion resistance and fracture characteristics has been demanded.
Conventionally, as a reinforcing filler for the tire tread, carbon black, silica, and the like have been used. Use of silica has an advantage of achieving the lowered hysteresis loss properties and the improved wet skid resistance. However, contrary to carbon black having a hydrophobic surface, silica having a hydrophilic surface has disadvantages such as small affinity with a conjugated diene rubber and dispersibility inferior to that of carbon black. For this reason, a silane coupling agent and the like need to be additionally contained in order to improve dispersibility and bond silica to the rubber.
Further, recently, attempts have been made to reduce hysteresis loss by introducing a functional group having affinity and/or reactivity with silica into a chain end of a rubber molecule having high mobility. The introduction of a functional group to the chain end can reduce the hysteresis loss by improving the dispersibility of silica in a rubber material, and further, by reducing the number of free polymer ends via bond with the filler particles. For example, Patent Document 1 discloses a modified diene rubber obtained by reacting a modifier having a glycidyl amino group with a polymer end, and Patent Document 2 discloses a modified diene rubber obtained by reacting glycidoxyalkoxysilane with a polymer end. Further, Patent Documents 3 to 7 disclose modified diene rubbers obtained by reacting alkoxysilanes containing an amino group with a polymer end, and compositions comprising these modified diene rubbers and silica.